The present invention relates to a process for producing optically active 3,7-dimethyl-6-octenol which contains from 2 to 10% by weight optically active 3,7-dimethyl-7-octenol and is useful as a material for perfumes, etc. The invention further relates to a process for producing a cis-3,7-dimethyl-2,6-octadienylamine compound (hereinafter referred to simply as xe2x80x9cnerylamine compoundxe2x80x9d) containing from 2 to 10% by weight cis-3,7-dimethyl-2,7-octadienylamine compound (hereinafter referred to simply as xe2x80x9cxcex1-nerylamine compoundxe2x80x9d), these amine compounds being intermediates for those optically active compounds.
The optically active 3,7-dimethyl-6-octenol provided by the invention, which contains from 2 to 10% by weight optically active 3,7-dimethyl-7-octenol, has an elegant rosy fragrance and is extremely useful for fragrance impartation to aromatic articles.
3,7-Dimethyl-6-octenol (hereinafter referred to also as xe2x80x9ccitronellolxe2x80x9d) has conventionally been known as a material for rosy perfumes, and the d-, l-, and dl-isomers have already come to be produced and practically used [Motoichi Indo, Gxc3x4sei Kxc3x4ryxc3x4 (Kagaku To Shxc3x4hin Chishiki), Kagaku Kogyo Nippo Sha, 1996] Such perfume substances are not limited to alcohols. These compounds, even when slightly different in structure, can generally have utterly different fragrances and differ also in properties, e.g., the ability to be retained and volatility. Consequently, for obtaining a new perfume, it is highly important to synthesize many compounds and investigate their fragrances.
Disclosed as processes for producing a nerylamine compound through the telomerization of isoprene with an amine compound are a method in which an n-butyllithium catalyst is used (JP-A-49-48610 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)), a method in which a catalyst prepared from a secondary amine, a conjugated olefin, and lithium metal is used (JP-A-51-4109), a method in which a catalyst prepared from a secondary amine, a polynuclear aromatic compound and/or a polyphenyl compound, and lithium metal is used (JP-A-53-135912), and a method in which a catalyst prepared from a secondary amine, a conjugated diene compound and/or polycyclic aromatic compound as an unsaturated hydrocarbon, a lithium salt, and sodium metal and/or potassium metal is used (U.S. Pat. No. 4,186,148).
However, the method disclosed in JP-A-49-48610 has the following drawbacks. The method necessitates a reaction time as long as from 5.5 to 24 hours despite the use of an n-butyllithium catalyst and has low selectivity to nerylamine. Consequently, it is difficult to apply the method to an industrial process for continuously conducting the reaction and this application is costly.
The method disclosed in JP-A-51-4109 has attained a yield as high as about 85% using a different lithium catalyst. However, a reaction time of 18 hours is necessary for attaining the yield. This method also is difficult to practice industrially.
The method disclosed in JP-A-53-135912 has succeeded in obtaining nerylamine in a yield of 86.4% by using a different lithium catalyst to react an amine with isoprene in a proportion of 1:5 at 80xc2x0 C. for 3 hours. However, since the isoprene amount is excessively large as compared with the amine amount, there have been problems concerning the recovery of isoprene and the yield of nerylamine.
The method disclosed in U.S. Pat. No. 4,186,148 has succeeded in obtaining nerylamine in a yield of 85% by reacting an amine with isoprene in a proportion of 1:5 first at 65xc2x0 C. for 1 hour and then at 80xc2x0 C. for 4 hours. However, since the isoprene amount is excessively large as compared with the amine amount, there have been problems concerning the recovery of isoprene and the yield of nerylamine. In addition, this method is unsuitable for continuous reaction because preparation of the lithium catalyst necessitates use of a dangerous metal such as sodium or potassium.
Furthermore, although JP-A-49-48610 discloses an N,N-dialkyl(3-methyl-2-butenyl)amine (formula 5), an N,N-dialkyl(2-methyl-2-butenyl)amine (formula 6), and an N,N-dialkyl(2-isopropenyl-5-methyl-4-hexenyl)amine (formula 7), which are yielded as by-products by the method disclosed therein, there are no descriptions therein concerning the xcex1-nerylamine represented by formula 4 in the invention. No descriptions concerning by-products are given in the specification of the other references cited above. 
In a conventional method for asymmetrically isomerizing a cis-dialkyloctadienylamine obtained, the amine is isomerized in tetrahydrofuran using a rhodium-BINAP catalyst and then hydrolyzed with sulfuric acid to obtain an aldehyde (see U.S. Pat. No. 4,604,474)
The present inventors made intensive investigations on methods for synthesizing optically active 3,7-dimethyl-6-octenol (citronellol), which is useful as a material for rosy perfumes. During these investigations, they have found that when the telomerization of an alkylamine with isoprene, which is known as a process for producing cis-3,7-dimethyl-2,6-octadienylamine (a nerylamine compound) serving as an intermediate for citronellol, is conducted under strictly selected reaction conditions, then cis-3,7-dimethyl-2,7-octadienylamine (an a-nerylamine compound) serving as an intermediate for optically active 3,7-dimethyl-7-octenol, which also is useful as a material for rosy perfumes, is yielded in a large amount.
The inventors have further found that asymmetrically isomerizing the mixture of nerylamine and xcex1-nerylamine in the same manner as in the reaction step of synthesis of citronellol from nerylamine, subsequently hydrolyzing the mixture, and reducing the resultant citronellal mixture gives a mixture comprising optically active 3,7-dimethyl-7-octenol and optically active 3,7-dimethyl-6-octenol (citronellol) and this mixture is more useful as a material for rosy perfumes than conventional ones. The invention has been completed based on this finding.
An object of the invention is to provide a process for stably producing optically active 3,7-dimethyl-6-octenol which contains from 2 to 10% by weight optically active 3,7-dimethyl-7-octenol and is extremely useful as a material for rosy perfumes. Another object of the invention is to provide a process for efficiently producing a cis-3,7-dimethyl-2,6-octadienylamine compound (nerylamine compound) containing from 2 to 10% by weight cis-3,7-dimethyl-2,7-octadienylamine compound (xcex1-nerylamine compound), these amine compounds being useful as materials for those optically active compounds.
The invention, which makes it possible to stably produce the above-described optically active 3,7-dimethyl-6-octenol (citronellol) containing from 2 to 10% by weight optically active 3,7-dimethyl-7-octenol, includes the following.
(1) A process for producing optically active 3,7-dimethyl-6-octenol, a compound having an excellent fragrance represented by formula (1), 
containing from 2 to 10% by weight optically active 3,7-dimethyl-7-octenol represented by formula (2): 
which comprises subjecting a mixture of an alkylamine and isoprene in a molar ratio in the range of from 1:4 to 1:4.5 to telomerization at a reaction temperature of from 80 to 100xc2x0 C. for from 2.5 to 3.5 hours in the presence of an alkyllithium catalyst and/or phenyllithium catalyst to thereby prepare a nerylamine compound represented by general formula (3): 
wherein R1 and R2 each represents a hydrogen atom or an alkyl, aralkyl, or aryl group having 1 to 10 carbon atoms, containing from 2 to 10% by weight xcex1-nerylamine compound represented by general formula (4): 
wherein R1 and R2 each represents a hydrogen atom or an alkyl, aralkyl, or aryl group having 1 to 10 carbon atoms, asymmetrically isomerizing the resultant reaction product mixture, subsequently hydrolyzing the mixture to obtain a citronellal mixture, and then reducing the citronellal mixture
(2) A process for producing a nerylamine compound represented by general formula (3): 
wherein R1 and R2 each represents a hydrogen atom or an alkyl, aralkyl, or aryl group having 1 to 10 carbon atoms, useful as an intermediate for 3,7-dimethyl-6-octenol, which contains from 2 to 10% by weight xcex1-nerylamine compound represented by general formula (4): 
wherein R1 and R2 each represents a hydrogen atom or an alkyl, aralkyl, or aryl group having 1 to 10 carbon atoms, which comprises subjecting a mixture of an alkylamine and isoprene in a molar ratio of from 1:4 to 1:4.5 to telomerization at a reaction temperature of from 80 to 100xc2x0 C. for from 2.5 to 3.5 hours in the presence of an alkyllithium catalyst and/or phenyllithium catalyst.
The invention will be explained below in detail Examples of the amine compound to be used in the invention include dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, cyclohexylamine, piperidine, pyrrolidine, and morpholine. Of these, dimethylamine, diethylamine, di-n-propylamine, and diisopropylamine are preferred.
The amount of the isoprene to be added is preferably from 3 to 5 times by mole, more preferably from 4 to 4.5 times by mole, the amount of the amine compound.
Examples of the lithium catalyst include methyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, and phenyllithium. Of these, n-butyllithium is preferred. The amount of the lithium catalyst to be used in the telomerization may be from 0.5 to 5 mol % based on the amine compound to be subjected to the reaction.
The telomerization reaction of the starting amine compound with isoprene for producing a nerylamine compound containing from 2 to 10%, preferably from 3 to 6% xcex1-nerylamine compound can be accomplished by introducing the lithium catalyst and the amine compound and isoprene as starting materials into the same reactor simultaneously or successively.
The reaction is conducted in an inert atmosphere with or without a solvent. In the case of using a solvent, the solvent is one in which the lithium compound used as a catalyst can dissolve. Examples of solvents which can be used include hydrocarbon solvents such as benzene and toluene and ether solvents such as tetrahydrofuran.
The temperature for the reaction is generally from 50 to 120xc2x0 C., preferably from 80 to 100xc2x0 C. The reaction is conducted for generally from 2 to 6 hours, preferably from 2.5 to 3.5 hours.
Subsequently, water, ethanol, CO2, or the like is added to the reaction mixture resulting from the telomerization of the starting isoprene with the starting amine compound conducted under the reaction conditions described above, whereby the lithium compound used as a catalyst is deactivated. Thereafter, the oil layer is distilled to thereby recover a nerylamine fraction containing from 2 to 10% xcex1-nerylamine compound.
The thus-obtained nerylamine fraction containing from 2 to 10% xcex1-nerylamine compound is subjected to an asymmetric isomerization reaction.
The asymmetric isomerization reaction is conducted in a solvent in an inert atmosphere such as, e.g., nitrogen using a known catalyst for asymmetric isomerization.
As the solvent may be used an ether such as tetrahydrofuran, a ketone such as acetone, or the like.
As the catalyst can be used a rhodium-phosphine complex catalyst (see JP-B-1-42959) or a catalyst such as [Rh(COD)(BINAP)]ClO4, [Rh(BINAP)2]ClO4, [Rh(BINAP)2]OTf, [Rh(COD)(t-BINAP)]ClO4, [Rh(t-BINAP)2]ClO4, or [Rh(t-BINAP)2]OTf, wherein xe2x80x9cBINAPxe2x80x9d means a 2,2xe2x80x2-bis (diphenylphosphino)-1,1xe2x80x2-binaphthyl group, xe2x80x9ct-BINAPxe2x80x9d means a 2,2xe2x80x2-bis (di-p-tolylphosphino)-1,1xe2x80x2-binaphthyl group, and xe2x80x9cOTfxe2x80x9d means a triflate group.
The reaction temperature is generally from 50 to 130xc2x0 C., preferably from 100 to 110xc2x0 C. After completion of the reaction, the reaction mixture is transferred to a distiller, where the solvent is removed by vacuum distillation to obtain a geranyl enamine compound (citronellal enamine compound) as an isomerization reaction product.
The geranyl enamine compound obtained by the asymmetric isomerization reaction is subjected to a hydrolysis reaction and thereby converted to a citronellal compound.
The hydrolysis reaction is an acid hydrolysis reaction. Although either an organic acid or an inorganic acid can be used as the acid, it is preferred to use an inorganic acid such as sulfuric acid or hydrochloric acid.
The hydrolysis reaction is conducted by dissolving the geranyl enamine compound in an inert solvent, e.g., toluene, and then adding an acid, e.g., sulfuric acid, to the solution to treat the enamine compound at a temperature of about from 0 to 10xc2x0 C. in an ordinary manner.
The citronellal compound obtained by the hydrolysis reaction is subjected to a catalytic hydrogenation reaction in an ordinary manner Thus, the citronellal compound, which is an aldehyde compound, is converted to an optically active citronellol compound which is an alcohol compound.
This reaction is conducted with stirring using a catalyst ordinarily used for reactions for hydrogenating aldehyde compounds into alcohol compounds, such as, e.g., a copper-chromium catalyst, palladium catalyst, or Raney nickel catalyst.
Finally, the catalyst is removed from the hydrogenation reaction mixture, which is then subjected to vacuum distillation. Thus, the target citronellol compound is obtained.